711
FXUS66 KOTX 012213
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
313 PM PDT Sat Jun 1 2024

.SYNOPSIS...
A dynamic system pushes across the region Sunday into Monday,
bringing widespread rain, followed by gusty winds, and the
potential for thunderstorms on Monday. Next week will see a
warming and drying trend. Confidence is increasing for
temperatures warming into the 80s and 90s.

&&

.DISCUSSION...
Tonight: In the wake of a weak shortwave passage from this
afternoon, some light showers will continue through the early
evening over the Idaho Panhandle. A westerly pressure gradient will
allow areas across the lee of the Cascades into the western Columbia
Basin to see breezy winds through the evening with gusts 25 to 35
mph.

Sunday and Monday: A strong late Spring storm remains on track to
impact the Pacific Northwest late Sunday morning through Monday.
Models have trended quicker with the onset of precipitation compared
to this time yesterday as a low pressure system approaches the
British Columbia coast. Aided by a rather strong jet with speeds
of 140 to 160 knots at its core, this system will transport an
atmospheric river into the region. Precipitable water values 175
to 200% of normal combined with strong upper level dynamics will
deliver moderate to heavy rainfall across much of the region late
Sunday morning through Monday afternoon. By late Monday morning
and afternoon, the focus will shift to widespread breezy to gusty
winds and the potential for thunderstorms across eastern
Washington and north Idaho.

RAIN: Precipitation totals through Monday evening will be between
1.50 to 3 inches for the Cascade crest. East of the crest, strong
westerly flow will work against significant accumulations, but could
see between 0.05 to 0.25 inches with areas such as Moses Lake and
Wenatchee showing a 75% chance of 0.10 inches of rain from 11 AM
Sunday to 11 AM Monday. When increased to 0.25 inches this potential
decreases to 25-30% for the Moses Lake area and 40% for Wenatchee.
Areas further north such as Omak and the Methow Valley are showing a
60-70% chance for 0.25 inches. As the system moves into far eastern
Washington and north Idaho, precipitation amounts will re-enhance
with around a 80% chance for above 0.50 inches of rain for Colville,
Spokane, Pullman, and Lewiston. Additionally, there is a 35 to 45 %
chance for these areas to see above 0.75 inches. Across the
valleys of Idaho Panhandle, there is nearly a 100% chance for over
0.50 inches, including Coeur d`Alene and Sandpoint. There is a
80% chance for over 0.75 inches at these locations and a 45%
chance for over an inch. Although this rain will be mostly
beneficial across the area given low river flows and dry soils,
there is an area of concern over central Idaho where the heaviest
rainfall is forecast. Smaller creeks and streams could see quick
rises, particularly in Lewis and Shoshone counties.

WINDS & THUNDERSTORMS: Winds will be breezy at the onset of
precipitation on Sunday through Monday morning, but will ramp up
late Monday morning and afternoon as the front moves across the
region. This will allow strong gusts to mix down the surface with
sustained 25-30 mph and gusts of up to 40-50 mph from the lee of
the Cascades across the Waterville Plateau, into the Moses Lake
Area, Spokane Area, Palouse, and lower Asotin and Garfield County.
Weak afternoon instability (MUCAPE 200-500 J/kg) combined with
the strong forcing and 30-45 knots of 0-6km shear could support
thunderstorm development across eastern Washington and north Idaho
Monday afternoon. The instability will be the limiting factor for
strong thunderstorm development, but any thunderstorms could
locally enhance antecedent surface winds with potential for minor
wind damage to small trees and branches. Winds will also result in
hazardous cross winds along north-south highways and loose
objects being pushed around. /vmt

Tuesday to Saturday: The Inland NW will transition to a drier and
warmer pattern through this period. Tuesday a zonal flow under a
strong jet will keep some clouds and shower chances alive around
the Cascades, the eastern third of WA and ID. Overall the best
precipitation chances will be in the mountains. Then chances wane
through the evening and overnight. It will remain breezy through
the day the day, with gusts near 20-30 mph, strongest near the
Cascades to the Upper Columbia Basin and West Plains, before
gradually waning heading into the late evening to overnight.

Wednesday to Friday will be drier with a ridge building in with
drier air. Winds will still remain slightly breezy Wednesday but
overall will be less than earlier in the week. Some upper impulses
slip by the southeast CWA later Friday, but for now the main
shower chances with that remains just south of our CWA until
Friday night and Saturday. Going into Friday night and Saturday
some of those impulses move into the region. These bring shower
and isolated t-storm chances to the Blues, Camas Prairie, L-C
Valley, Palouse and Panhandle Mountains Friday night. Confidence
is low, but at least some risk is there.

The more notable feature will be warming temperatures. Temperatures
Tuesday remain below normal, then warm closer to normal Wednesday.
Then Thursday into Saturday temperatures warm above normal in a
more notable way. While there are is some disagreement on precise
numbers, maybe areas are forecast to warm to between 85-95
degrees, with the warmer readings in the lee of lee-side zones,
deeper Columbia Basin and L-C Valley. However guidance even has
between a 20-40% chance of reaching near over the Palouse and
Spokane area by the end of the week too. So I am saying there is a
chance, with that chance higher toward downtown Spokane. The heat
risk rises to a moderate level by Friday and Saturday, though
temperatures may dip slightly Saturday with more moisture and
clouds in the region. This means some precautions may be needed to
stay cool. /Solveig

&&

HYDROLOGY...
An Areal Flood Watch has been issued for Lewis and Shoshone
Counties in Idaho. Heavy rainfall forecast over the Clearwater
Mountains will result in increased snowmelt and bring sharp rises
to small creeks and streams in these areas. Additionally, the amount
of water with a little bit of snow left to be melted in the
highest elevations of the Cascades will result in a steep rise on
the Stehekin River. For the rest of the forecast area, rain will
be largely beneficial due to antecedent dry soils and low base
river flows. Flooding is not anticipated at this time on larger
rovers but will need to be monitored. Another potential impact
will be for rock slides on steeper slopes in the Cascades and
across the Idaho Panhandle.

&&

.AVIATION...
18Z TAFS: An upper level trough moving through the Inland
Northwest this morning is bringing widespread overcast skies and
isolated spots of very light precipitation. Conditions are
expected to remain VFR through the next 24 hours. There is a 20%
chance for thunderstorms near the Canadian border this afternoon.
Thunderstorms are expected to remain north of airports from the
Methow Valley, Omak, Colville, and Sandpoint. Model soundings
across northeast Washington and north Idaho keep convective cloud
tops below 20kft, which may limit lightning development. Winds
will pick up out of the west into KEAT Saturday afternoon and
evening with sustained winds up to 15 knots and gusts up to 25
knots.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: High confidence in
VFR conditions and thunderstorms remaining north of TAF sites.

-----------------------

Confidence descriptors:
Low - Less than a 30 percent chance
Moderate - 30 to 70 percent chance
High - Greater than a 70 percent chance

For additional probabilistic information for NWS Spokane airports,
please refer to the Aviation Dashboard on our webpage:
https:/www.weather.gov/otx/avndashboard

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        49  65  51  63  43  66 /  10  50 100  90  20  30
Coeur d`Alene  48  63  51  59  43  61 /  10  60 100 100  30  40
Pullman        48  64  50  59  42  63 /  10  50 100  90  20  30
Lewiston       54  72  58  69  50  73 /  10  50 100 100  10  20
Colville       42  65  44  62  36  63 /  30  70 100 100  30  40
Sandpoint      47  61  49  56  42  57 /  20  60 100 100  60  60
Kellogg        51  62  51  55  45  58 /  20  60 100 100  50  60
Moses Lake     50  68  51  69  47  74 /  10  60  80  50  10  10
Wenatchee      53  66  53  64  49  68 /   0  70  80  50  20  30
Omak           48  67  49  68  44  71 /  10  60  90  60  10  20

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...Flood Watch from Sunday afternoon through Monday evening for
     Central Panhandle Mountains-Lewis and Southern Nez Perce
     Counties.

WA...None.
&&

$$